ice: Add feature bitmap, helpers and a check for DSCP

DSCP a.k.a L3 QoS is only supported on certain devices. To enforce this,
this patch introduces a bitmap of features and helper functions.

The feature bitmap is set based on device IDs on driver init. Currently,
DSCP is the only feature in this bitmap, but there will be more in the
future. In the DCB netlink flow, check if the feature bit is set before
exercising DSCP.

Signed-off-by: Anirudh Venkataramanan <anirudh.venkataramanan@intel.com>
Tested-by: Gurucharan G <gurucharanx.g@intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>